Gas analyzer



Jan. 12, 1943. E J, NORTON f 2,307,800

GAS ANALYZER Original Filed July l,v 1939 Figi 33 0.2 PRESSURE IN mmHg/ H ZQ VAPOR PRESSURE Hz PRESSURE R26- rlg. 7 ZZ Z5 Ill] 2' lrvehtor:

Francis J. Norton, 2o l is Attorney.

Patented Jan. 12, 1943 UNITED STATES PATENTy OFFICIELy 2,307,800 GAS ANALYZEB Francis J. Norton,

General Electric New York original appummn my 1,

282,418. Divided and this application 1940, serial No. 330,311

(c1. vs -s1) i It is an object of my invention to provide an improved, simplified apparatus and method for y gas analysis in which definite accurate indications may readily be obtained. l

The objects oi my invention include .the utilization for gas analysis of equilibrium reactions between gases and metals. Moresp'eciiic objects of my invention are to provide methods and apparatus for measuring percentages of hydrogen in hydrogen atmospheres.

Other and further objects and advantages will become apparent as .the description proceeds.

In carrying out my invention in its preferred form a suitable metal is exposed to a gas mixture to be analyzed and so arranged that it will have a temperature gradient such that an equilibrium reaction with the active gas constituent of the atmosphere to be analyzed will take place and the temperature point at which the reaction is in equilibrium will indicate the percentage oi active gas in the mixture. In the case of determination of the oxygen content in gas mixtures one portion of a non-uniformly heated metal will be in one state, that -is oxidized, and another portion will be in another state, that isV bright or nonoxidized, and the position of the sharp dividing line between these two areas serves as a measure of the gas composition.

The invention will be understood more readily from the following detailed description when considered in connection with the accompanying drawing andthose features o! the invention which are believed to be novel and patentable will be pointed out in the claim appended hereto. In the drawing Figure 1 is a side view of apparatus forming one embodiment of my invention with the electrical connections omitted. Figure 2 is a circuit diagram of the apparatus oi- Figure 1 showing portions thereof schematically. Figure 3 is a graph explaining. the principle of operation of one embodiment ofthe invention. Figure 4 is a plan view of another embodiment of' the invention placed on' the sheet with its temperature scale in line with that o! the graph of Figure. Figure 5 is a graph illustrating the principle of operation of my invention in con- Schenectady, N. Y., assigner to Company, a corporation of 1939, Serial No. June 7,

nection with the analysis of diereut gas from that represented' in Figure 3. Figure 6 is a schematic diagram of still another embodiment of my invention. Figure 'l is a detail plan view of the heated disk utilized in the apparatusof Figure 6 and Figure 8 is a schematic diagram ofA an embodiment of my invention operating on the blmetallic principle.

Although my invention is applicable to the analysis of various diilerent gases, its principle will, for the sake of illustration, be explained in greatest detail in connection with the determination of oxygen content in gases. In central station operation, it is important to control combustion and have a minimum amount lof excess oxygen in the exitl gases. My4 invention lends itself to a convenient and continuous indication y oi the exact oxygen content. A strip oi a suit` able metal exposed to the gas to be analyzed is heated in such a manner that the temperature varies progressively along the length of the strip, and the position of the line of demarcation between the portion oi the material at its surface which is combined with the gas and the portion which is not combined with .he gas is determinedin order to obtain a, measure of the gas content. The strip may be conveniently heated by its own resistance as a result of passing current through it. In order to obtain a temperature gradient along the length of the strip, .the strip may be tapered, as illustrated by the strip Il shown in Figure 4, or may be tapered symmetrically as are the strips in Figure 1. For oxygen analysis the strip is composed of a suitable material, 'such as palladium, for example, which has an equilibrium reaction with oxygen varying according to temperature.

In Figure 3, the curve l2 represents the relationship between the dissociation pressure oi palladium oxide and temperature. Curve l2 is plotted with degrees of temperature Centigrade along the vertical axis and millimeters of mercury dissociation pressure along the horizontal axis. It will be apparent that, for any temperature above or to the left of the curve, palladium and oxygen do not combine or remainn combination and lthe palladium remains bright, whereas for any temperature beloar the curve or any to the right of the curve palladium and oxygen combine and the strip of palladium is darkened by oxidation of its surface. If a gas mixture oi. nitrogen and oxygen containing 5% oxygen by volume, or a partial pressure of 38 mm. of oxygen point a), is passed over the nonuniiormly heated strip li, ailthe points on the strip a" which is at '136 centigrade win be oxidized since they are below the dissociation pressure of palladium oxide at '736 centigrade, which is 38 mm. All points above a" on the strip will be bright, since they are above the dissociation gen, 90% nitrogen, or a partial pressure of '16 mm. oxygen, the equilibrium line on the strip moves up to point b" which is at 764 centigrade where the dissociation pressure of palladium oxide is 76 mm. The line I4 at b" indicates that there is sufiicient oxygen for a dissociation pressure of 76 mm. or 10% oxygen. The moveequilibria involving sulphides instead of oxides would be employed and in connection with carment of the equilibrium line constitutes a pointer along a temperature scale and gives a quantitative measure of oxygen in the gas mixture. /All points below the line are dark, due to oxide,and

all points above are bright due to unoxidized metal. By referring to the graph of Figure 3 and bearing in mind that the ratio of partial pressure of the oxygen in a gas mixture to atmospheric pressure equals to the fraction of oxygen in the mixture measured by volume or in gram-molecules, the distances along the strip II corresponding to different percentages of oxygen may be determined and a suitable scale may be placed beside the strip II so that direct readings of oxygen percentage maybe obtained.`

In an exactly similar way an iron strip can be used to indicate the composition of mixtures of water vapor or steam and hydrogen. In the graph of Figure 5, the curve I5 represents the 4relationship between the ratio of water to hydrogen in the surrounding atmosphere and the temperature at which iron oxide dissociates. Curve I6 represents the relationship between the ratio and the temperature at which iron oxide passes from FeO to Fe304 and vice versa. The curves are plotted with degrees of temperature centigrade along the vertical axis and the ratio of water vapor pressure to hydrogen pressure along the horizontal axis. The line I5 on the equilibrium diagram is the one marking the dark oxide, bright metal boundary, and changes in` water' content of hydrogen can be followed just as the oxygen content was followed on a. palladium strip. The area to the left of the line I5 represents a bright condition of the iron, whereas the area to the right representing the oxide condition is divided` into two parts with the one above theI line I$- representing FeO and that below the line I6 representing FeaOl. In either case, however, the region tofthe right o f the line I5 represents oxidation. The point -I'I along the line I5 representing an HzO/Hz ratio of 2/10,'has an equilibrium temperature of 480 centigrade, and this will be marked by a line on the strip, such as the strip II, with ldark iron oxide at temperatures below 480 centigrade and a bright reduced iron surface at temperatures above 480 centigrade.

'Although I have described the invention for the sake of illustration in connection 4with the analysis vof two different speciilc'types of gas mixtures and utilizing twodifferent specific metals, it will be. understood that rmy invention is not limited thereto, and includes analysis of any gas which has an equilibrium reaction with a solid material varying-'in accordance with variations. in temperature. For example,4 in the analysis of hydrogen sulphide,

ated by a gas indicator in accordance with myv invention, the arrangement of Figure 6, for example, may be employed in which a disk I8 is heated at the center in any suitable manner as by means of an electrical resistor I9 attached thereto or current is passed through the center of the disk itself, and the disk I8 is placed within a tube 20 through whichthe gas to be analyzed is passed. A Considered as an oxygen content analyzer, variations in the gas content will produce an oxide ring on the disk I8 like an iris diaphragm varying with changing gas composition. `As shown in Figure 7 the outer oxidized portion 'pf the 'disk I8 will form a dark ring, whereas the center. unoxidized portion will form a bright circle, the area of which latter increases as the oxygen content decreases. The bright area may be measured in any suitable manner as by reflection of light from a lamp 2l impinging upon a photocell 22 or a photoelectric relay device. As will be well understood by those skilled in the art, the output of the photocell 22 varies withthe amount of light received thereby, and a suitable current responsive device, such as a measuring instrument or relay 23 may be provided for giving indications of oxygen content or for operating controlling apparatus, not shown, for restoring conditions of controlled apparatus -to bring about the desired oxygen ratio.

In utilim'ng my invention in connection with the use of controlled gas atmospheres for bright annealing of steel, for example, a strip such as that shown in Figure 4 is employed to indicate to what extent and to what temperatures the atmosphere is reducing and just where oxidation will start, as was described for the iron strip. The strip may be heated either indirectly or directly, e. g. 'by passing current through it as already explained. The strip is of the same composition as the steel which is to be annealed and microscopic examination, after polishing and etching such a heated strip, will tell to what steel used for the strip. After such a calibration for carburization, the position of a discontinuity on the heated taperedV strip will tell the temperature at which the eilect is taking place. The original line of demarcation may not be as sharp as in the case of oxygen analysis in nue gases, previously discussed, but after calibration of the -strip polishing, etching and microscopic examination will be unnecessary except for exceedingly precise determinations.

Another electrical arrangement for obtaining deecting-pointer indication or for controlling electrical circuits in accordance with lvariations in gas analysis is shown in Figures 1 and 2. In this embodiment of my invention a Wheatstone bridge is constructed, composed of two opposite arms 25 and 26 of a relatively inert metal, such as platinum, 'and two other opposite arms 21 and 28-of a metal having an equilibrium reaction with the active constituent of the gas to be let 33 through which gas to be analyzed is passed so as to pass over the palladium strips 21 and 28. Two opposite points 34 and 35 of the Wheatstone bridge are connected to a suitable source of current 36 which serves both to heat the bridge arms and to permit determination of electrical balance of the bridge by means of an electrical instrument. Preferably for the sake of adjusting the bridge a resistor 31 is provided between two of the adjacent arms of the bridge, for example, the strips 25 and 28 and an adjustable tap 88 serves as one of the ends of the diagonal arm of the bridge. For determining bridge balance, a currentresponsive device, such as a measuring instrument or a relay 39 is provided which is connected between the adjustable tap 38 and the opposite diagonal point 48 of the bridge so that the device 39 serves as a diagonal arm of the bridge.

As explained in connection with the apparatus of Figure 4, variations inv oxygen content of the gas passing through the tube 3| result in the formation of greater or less amounts of oxide surface along the tapered portion of the strips 21 and 28 causing the lengths of the bright portions 29 and 88 to vary accordingly. The variation in the relative lengths of the bright and dark portions of the strips 21 and 28 changes the heat radiated by the strips since the oxidation increases the'thermal emlssive power of the metal surface. The increase in the heat radiated results in a decrease in temperature of the strip and consequently a reduction in the resistance thereof. The resultant unbalance of the bridge measured by the instrument 39 depends upon the oxygen content and accordingly the instrument 39 may be calibrated in terms of oxygen percentage. Such factors as ambient temperature and thermal conductivity of the gas, unrelated to oxygen content, are balanced out by virtue of the use of the platinum strips 25 and 26 of similar dimensions and resistance to the strips 21 and 28.

Instead of arranging the platinum and palladium strips or other dissimilar strips as the arms of a Wheatstone bridge as illustrated in Figures i and 2strips of two dierent metals, such as platinum and palladium may be welded or otherwise joined together back to back to form a bimetal strip 4I, as illustr-ated in Figure 8. The bimetal strip 4l may be heated in any desired manner as by passing a current through it by means of electric leads 42 and 43, the latter of which is exible in order that the bimetallic strip and this expansion,

composition. An increase in 4l may be supported from one end, e. g., the lower end 44 and permit the other end 45 to deflect. As previously explained, the bimetallic strip may be tapered and the changes in extent of oxidized surface and emissivity of the palladium surface 21 in response to variations in gas composition will vary the temperature of the palladium strip 21, thus varying the degree of expansion and causing the end 45 of the strip 4l to deflect in one direction or the other according to the gas extent of darkened surface, indicating increased oxygen content, will increase the heating radiation, thus lowering the temperature and shortening the palladium side of the bimetal strip to cause bending in that direction. Suitable means may beprovided for indicating the position of the end 45.' This deiiection may, if desired, be amplied mechanically or otherwise, for example, by means of a rack 46 carried at the end 45 of the strip 4|, a'ipivo'tally mounted' pinion '41 engaging the rack 46, and a pointer 48 carried by pinion 41,-Y a scale 49 being provided to cooperate with the pointer 48.

In connection with the measurement of hydrogen percentages the bimetallic strip 4I of Figure 8 may also be employed. However, in this case it is unnecessary for the strip 4I to be tapered and the heating circuit with the leads 42 and 43 may be omitted, if other means are employed to maintain the strip at an adequate temperature for hydrogen absorption. Since hydrogen dissolves in palladium there is an expansion of the metal due to actual change in lattice structure increasing with the concentration of hydrogen, strip 4I to -deflect in accordance with the percentages in the gas being-analyzed. The absorption of hydrogen'takes place particularly at approximately red heat. In order to guard against temperature eiects, the heating current is kept constant or other means are employed for assurance of constant temperature.

I have herein shown and particularly described certain embodiments of my inventionand certain methods of operation embraced therein for the purpose of explaining its principle and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possible and I aim, therefore, to

cover all such modifications and variations as fall within the scope of my invention which is `deiined inthe appended claim.

What -I claim as new and desire to secure by Letters Patent of the United States, is:

A hydrogen analyzer comprising a bimetallic strip, means for passing a gaseous mixture assumed to contain hydrogen over the surface of said bimetal, andan indicator responsive to the bending of the bimetal, the bimetal comprising palladium and platinum, whereby variations in the hydrogen content-vary the hydrogen absorption in the palladium thereby causing expansion and contraction thereof to bend the bimetal.

' FRANCIS J. NORTON.

will cause the bimetallicl K Itis 'cerilzfiedtat error appears. the printed spebificgtiph of the above n'aau'uberod. pat-:nent re'quring correction as fol-10min; Page 1, sc- A out *,to; and thgtzhe sgiid Batters lltent hld4 b'pogdwith this corieccipn 'th'rein that'thdsme may confor-mitad 'gna record bringe case m the intent AQgnce.

signed and enea ,this 25rd any f Fabiyuuy, A, D. 1915, 

